The present disclosure relates to optical systems for fluorescence detection and fine particle analyzing apparatuses. In particular, the present disclosure relates to an optical system for detecting a plurality of fluorescent light beams and a fine particle analyzing apparatus that includes the optical system.
In general, an optical measuring method using flow cytometry (a flow cytometer) is utilized when identifying biological fine particles such as cells, microorganisms, liposomes, and the like. Flow cytometry is an analytical method for identifying a plurality of fine particles one by one by irradiating the fine particles, which flow through a flow path in a line, with a laser beam of a specific wavelength and by detecting fluorescent light beams and scattered light beams emitted from each of the fine particles.
In particular, a laminar flow is formed from a sample liquid that includes fine particles, which are to be measured, and a sheath liquid that flows at the periphery of the sample liquid in a flow path in order to arrange the plurality of fine particles included in the sample liquid in a line. When a laser beam is irradiated onto the flow path in this state, the fine particles pass across the laser beam one by one.
In this case, the fluorescent light beams and the scattered light beams emitted from each of the fine particles excited by the laser beam are detected by a light detector such as a charge coupled device (CCD) or a photomultiplier tube (PMT). Then, the light beams detected by the light detector are transformed into electrical signals and converted into numbers. Then, the types, sizes, and structures of the individual fine particles are determined by performing a statistical analysis.
Since fluorescent light beams emitted from biological fine particles such as cells are weak, it is necessary that the fluorescence detection performance of a flow cytometer that analyzes these particles be high. In particular, there is a need to improve the sensitivity of fluorescence detection in multi-beam measurement in which samples are irradiated with a plurality of excitation light beams of different wavelengths, and the resulting plurality of fluorescent light beams are detected.
In the field of light detection, methods for improving detection performance include, for example, a method for detecting fluorescent light beams emitted from samples after amplifying the fluorescent light beams with an optical amplifier (see, Japanese Unexamined Patent Application Publication No. 2010-099095) and a method for electrically correcting a detected signal (see, Japanese Unexamined Patent Application Publication No. 2011-232259). Hitherto, optical systems for light detection using a parabolic mirror or an elliptical mirror as a reflecting mirror have been proposed (see, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2001-509266 and Japanese Unexamined Patent Application Publication Nos. 2003-329590 and 2002-162350 (hereinafter referred to as “Patent Document 3”, “Patent Document 4”, and “Patent Document 5”)).
In the optical systems for light detection of the related art described in Patent Documents 3 and 4, samples are disposed in the vicinity of a focal point of a parabolic mirror, and the parabolic mirror causes light beams emitted from the samples to become parallel light beams, and the parabolic mirror emits the light beams to a detector. In the fluorescence measuring apparatus described in Patent Document 5, fluorescent light beams emitted in various directions from samples are converged on an incidence plane of a detector by a parabolic mirror and an elliptical mirror.